Variable stiffness coil for vasoocclusive devices

Abstract

The variable stiffness vasoocclusive coil is given variable stiffness along the length of the coil by selectively heat treating certain segments of a primary or secondary coil. The primary coil can be selectively heat treated to form soft or deformable segments along the length of the coil, and can then be shaped into a secondary shape that is set by a heat treatment process. Distal regions of the coil can also be heat treated to make the distal ends of the coil softer, more deformable, or less traumatic.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThis invention relates generally to implantable devices for interventional therapeutic treatment or vascular surgery, and more particularly concerns a variable stiffness vasoocclusive coil that exhibits variable stiffness along the length of the coil.2. Description of Related ArtThe art and science of interventional therapy and surgery has continually progressed towards treatment of internal defects and diseases by use of ever smaller incisions or access through the vasculature or body openings in order to reduce the trauma to tissue surrounding the treatment site. One important aspect of such treatments involves the use of catheters to place therapeutic devices at a treatment site by access through the vasculature. Examples of such procedures include transluminal angioplasty, placement of stents to reinforce the walls of a blood vessel or the like and the use of vasoocclusive devices to treat defects in the vasculature. There is a...

AI Technical Summary

Benefits of technology

Briefly, and in general terms, the present invention provides for a variable stiffness vasoocclusive coil that exhibits variable stiffness along the length of the coil. Variable stiffness is accomplished by selectively heat treating certain segments of a primary or secondary coil. The primary coil can be selectively heat treated to form soft or deformable segments along the length of the coil, and can then be shaped into a secondary shape that is set by a heat treatment process. A secondary coil such as a three dimensional coil can be produced with variable stiffness through a selective heating of localized segments of the coil. Distal regions of the coil can also be heat treated to make the distal ends of the coil softer, more deformable, or less traumatic. Upon deployment, the coil will take on its pre-formed three dimensional shape, and will deform in a random three-dimensional shape to conform to the shape of the vessel or malformation into which the coil is introduced. The variable stiffness coil is advantageously formed of a shape memory metal, and variable stiffness can be achieved through aging of desired segments of the shape memory metal coil to raise the parent phase or Austenite phase finish temperature, thus making the treated segments of shape memory metal softer and more flexible.

The invention also provides for a method for making a variable stiffness occlusive coil for use in interventional therapy and vascular surgery adapted to be inserted into a portion of a vasculature for occluding the portion of the vasculature of a patient, comprising the steps of providing a coil formed from one or more flexible strands of a shape memory metal, the coil having a primary coil configuration and an initial stiffness; and heat treating a plurality of segments of the coil to cause the plurality of segments to have reduced stiffness. In one presently preferred embodiment, the step of providing a coil comprises heating the coil in a desired three dimensional configuration to set the three dimensional shape. In a preferred aspect of the method of the invention, the shape memory metal has an Austenite phase finish temperature, and the step of heating the coil comprises heating the coil at about 475° C. to 525° C. for about 1 to 20 minutes to set the Austenite phase finish temperature of the coil to about −5° C. to 10° C. The step of heat treating the coil can be accomplished by artificially aging a plurality of segments of the coil to raise the Austenite phase finish temperature to about 35° C. to 50° C., such as by heating a plurality of segments of the coil to a temperature of about 400° C. for a period of about 5 seconds to 30 minutes.

Problems solved by technology

However, substantial risks to a patient are involved in such a procedure, and a coil which has soft or deformable segments may offer less risk to a patient.

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